EL400

FN7156 Rev 0.00

Page 6 of 9

Sep 20, 2002

Equivalent Circuit

Burn-In Circuit

Applications Information

Theory of Operation

The EL400 has a unity gain buffer from the non-inverting input

to the inverting input. The error signal of the EL400 is a current

flowing into (or out of) the inverting input. A very small change in

current flowing through the inverting input will cause a large

change in the output voltage. This current amplification is called

the transimpedance (ROL) of the EL400 [VOUT = (ROL)*(-IIN)].

Since ROL is very large, the current flowing into the inverting

input in the steady-state (non-slewing) condition is very small.

Therefore we can still use op-amp assumptions as a first-order

approximation for circuit analysis, namely that:

1. The voltage across the inputs is approximately 0V.

2. The current into the inputs is approximately 0mA.

Resistor Value Selection and Optimization

The value of the feedback resistor (and an internal capacitor)

sets the AC dynamics of the EL400. The nominal value for the

feedback resistor is 250

, which is the value used for

production testing. This value guarantees stability. For a given

All Packages Use The Same Schematic.